Many applications exist for refrigeration systems including residential, commercial, and industrial applications. For example, a commercial refrigeration system may be used to cool an enclosed space such as a data center, laboratory, supermarket, or freezer. Very generally, refrigeration systems may include circulating a fluid through a closed loop between an evaporator where the fluid absorbs heat and a condenser where the fluid releases heat. The fluid flowing within the closed loop is generally formulated to undergo phase changes within the normal operating temperatures and pressures of the system so that considerable quantities of heat can be exchanged by virtue of the latent heat of condensation and vaporization of the fluid.
Refrigeration systems may operate with a free-cooling system or loop when ambient temperatures are low. The free-cooling system may exploit the low temperature of the ambient air to provide cooling without the need for an additional energy input from, for example, a compressor, a thermoelectric device, or a heat source. Typically, free-cooling systems may employ a separate heat exchanger or portion of a heat exchanger coil when operating in a free-cooling mode. When free-cooling is not desired, or feasible, the separate heat exchanger or coil portion may not be utilized.
In an air-cooled condenser, the refrigerant flowing through the condenser can exchange heat with circulating air generated by an air moving device such as a fan or blower. Since circulating air is used for heat exchange in an air-cooled condenser, the performance and efficiency of the condenser, and ultimately the HVAC&R system, is subject to the ambient temperature of the air that is being circulated through the condenser. As the ambient air temperature increases, the condensing temperature (and pressure) of the refrigerant in the condenser also increases. At very high ambient air temperatures, i.e., air temperatures greater than 110 degrees Fahrenheit (° F.), the performance and efficiency of the HVAC&R system can decrease due to higher condensing temperatures (and pressures) caused by the very high ambient air temperatures.
Some projects require chilled water year round (data centers, process applications) at a relatively warm chilled water temperature (between 7° C. and 15° C.). When ambient temperature is lower than required chilled water temperatures, free-cooling becomes a more efficient solution than mechanical cooling. It would be beneficial for a free-cooling option to offer the possibility to operate the chiller in mechanical cooling mode with no loss of efficiency, allowing the free cooling loop to draw heat from a mechanical refrigeration loop. It would also be beneficial to use the free-cooling loop as the unique source of cooling when working in free-cooling only mode.